A rail vehicle is provided with a drive system, which is disposed under the floor of the vehicle and mainly includes a truck frame, a main motor placed on the truck frame, and a gear unit coupled to the main motor and a large-gear shaft. The gear unit reduces the number of rotations of the main motor and transmits the driving force to the large-gear shaft.
The gear unit incorporates in its inside a high-speed small gear fixed to a small-gear shaft, a low-speed large gear fixed to the large-gear shaft and in mesh with the small gear, and a gear case housing the small gear and the large gear.
The small gear and the large gear are retained in the gear case with bearings arranged at both ends of the gears in such a manner that the axes of the small gear and the large gear are parallel with each other. Tapered roller bearings, which are conical, and are capable of supporting radial and thrust loads and have large allowable loads, are used as these bearings.
To use a tapered roller bearing appropriately, it is important to manage the axial clearance (end play) between the bearing outer ring and the tapered rollers. In general, such end play is measured during the assembly at a plant and on other occasions with a dedicated measurement apparatus.
In a conventional technique described in Patent Literature 1, a gear unit is placed on a measurement stand and its gear case is pushed and polled with a load applied in the axial direction of the rotation shaft. A relative displacement of the large-gear shaft and the gear case in the axial direction is obtained by this operation. This relative displacement is measured as the end play of a tapered roller bearing.